Interspecific effects of grey squirrels (Sciurus carolinensis) on the space use and population demography of red squirrels (Sciurus vulgaris) in conifer plantations

Interspecific competition between red squirrels and grey squirrels was inve stigated by comparing the population demography, spacing behavior and habit at use of red squirrels in two large conifer plantations in northern Englan d: one site had only red squirrels (the 'red-only' site), in the other both red and grey squirrels occurred (the 'red-grey' sire). Despite more abunda nt food at the red-grey site, red squirrel densities (0.26 ha(-1) at the re d-grey site, 0.29 ha(-1) at the red-only site), adult survival rates and th e breeding rates of females were similar at both study sites. Grey squirrel s at the red-grey site occurred at higher densities (0.92-1.1 ha(-1)) than did the reds and tended to have higher breeding rates. In the presence of g rey squirrels, the recruitment pattern of red squirrels changed and there w as little recruitment of subadults. The juvenile recruitment rate in the re d-grey site (13%) was much lower than in the red-only site (50%). Grey squi rrels, in contrast, had higher juvenile recruitment rates at the red-grey s ite (41%). The core areas of the home ranges of red squirrels in the red-gr ey site were more strongly overlapped by grey squirrels than by conspecific s. Red squirrels did not select the habitat with the best tree seed crop (S cots pine) but preferred dense Sitka spruce plantations; they appeared to a void the Scots pine area with its high grey squirrel density. Data on foot length and body condition indicated decreased body growth in young red squi rrels when grey squirrels were present. Our data suggest that adult red squ irrels suffered little from interspecific competition with grey squirrels a nd that the key factor is decreased juvenile recruitment in red squirrels.